1. Field of the Invention
The present invention relates to a method and apparatus for controlling a swivel angle of headlights of a vehicle.
2. Description of the Related Art
A variable light distribution front-lighting system (referred to as an adaptive front-lighting system [AFS]) including a headlight and a controlling device is conventionally known. The headlight is configured such that an optical axis of the headlight (in other words, an irradiating direction of irradiation light) can be turned within an angular range in a vehicle width direction. The angular range is preset in advance. The controlling device performs swivel control to turn the optical axis of the headlight in the vehicle width direction in accordance with a steering angle of a vehicle (in other words, changes the irradiating direction). Hereinafter, an angle of the irradiating direction to a direct advance direction is referred to as a swivel angle. The irradiating direction is the direction in which the irradiation light, is irradiated. The direct advance direction is a direction in which the vehicle is traveling straight. A maximum swivel angle by which the optical axis can be turned is referred to as a saturated angle.
In this type of AFS, as shown in FIG. 5A, when a steering angle exceeds a first preset steering angle (α1 in FIG. 5A), preset in advance, as a result of a steering wheel being turned, the swivel angle increases in accordance with the steering angle. When the steering angle exceeds a second preset steering angle (α2 in FIG. 5A) which is preset in advance, the swivel angle is maintained at a saturated angle. When the steering wheel starts to return from a steering angle at which the swivel angle is saturated (α3 in FIG. 5A; referred to, hereinafter, as a saturated steering angle) to a steering angle at which the vehicle travels straight (referred to, hereinafter, as a neutral steering angle), the swivel angle is maintained at the saturated angle until the steering angle is at the second preset steering angle. When the steering angle becomes less than the second preset steering angle, the swivel angle decreases in accordance with the steering angle such that the optical axis of the headlight is in the direct advance direction of the vehicle when the steering angle is at the first preset steering angle (this swivel angle is referred to, hereinafter, as a neutral swivel angle). Hereinafter, a swivel control performed when the steering wheel is returned from the saturated steering angle to the neutral steering angle is referred to as a “return swivel control.”
However, when a return swivel control such as that described above is performed, the swivel angle does not immediately change when a driver steers the steering wheel to return the steering wheel. Therefore, the driver experiences inconvenience because the return of the headlight is slower than the steering operation.
Thus, a following return swivel control is proposed (refer to, for example, Japanese Patent Application Publication (Laid-open) No. 2004-51043). As shown in FIG. 5B, when the steering wheel starts to return from the saturated steering angle to the neutral steering angle, the swivel angle decreases in accordance with the decrease in the steering angle such that the swivel angle is at the neutral swivel angle when the steering angle is at a third preset steering angle (α4 in FIG. 5B) which is greater than the first preset steering angle (α1 in FIG. 5B), without the swivel angle being maintained at the saturated angle.
In other words, in the AFS described in Japanese Patent Laid-open Publication No. 2004-51043, the return swivel control is performed using a swivel angle that is uniquely determined in accordance with a steering angle at the time of when the steering wheel starts to return (more accurately, the saturated angle at the time of when the steering wheel starts to return) and the third preset steering angle, based on a swivel relationship in which the steering angle and the swivel angle are associated in advance (this return swivel control is referred to, hereinafter, as a specified swivel control).
Among the AFS, an AFS exists in which the return swivel control is performed as follows (this swivel control is referred to as an “ordinary swivel control”). Upon the first preset steering angle and the second preset steering angle being changed based on a speed of an own vehicle, the swivel angle is maintained at the saturated angle until the steering angle is at the second preset angle. When the steering angle is less than the second preset angle, the swivel angle becomes the neutral swivel angle when the steering angle is at the first preset steering angle.
When the specified swivel control described in Japanese Patent Laid-open Publication No. 2004-51043 is applied to an AFS such as that described above, when the steering wheel starts to return from the saturated steering angle to the neutral steering angle, the swivel angle becomes closer to the neutral swivel angle in accordance with the steering operation. Therefore, the possibility of the driver experiencing inconvenience caused by a delay in the return of the irradiating direction of the headlight and the like can be reduced.
However, after the steering wheel returns from the saturated angle by a certain amount, the swivel angle may return to the neutral swivel angle more quickly when the ordinary swivel control is used to control the swivel angle, compared to when the swivel angle is controlled by the specified swivel control. A swivel control matching the senses of the driver may not be performed.
In other words, in the conventional AFS, when the steering wheel starts to return from the saturated steering angle to the neutral steering angle, a swivel control matching the senses of the driver can be performed. However, after the steering wheel returns from the saturated angle by a certain amount, the swivel control matching the senses of the driver may not be performed.